COMPLETE PIECES OF TRANSISTOR APPARATUS 



permissible collector dissipation for the transistor used; but notice also 

 that the high collector voltage to which the transistor is subjected at point C 

 is related to Vg by the turns ratio rig between L^ and L^. Typically, a tran- 

 sistor might have a maximum permissible collector voltage of 30. If the 

 battery voltage is 12, then the maximum voltage which may occur across L^, 

 during the collapse phase is 18. Hence if n^ = 50, care must be taken that 

 Rj^ is never so high that V^ is allowed to exceed 900 V. 



/?^ moderate 



R, low 



out 



Output current 

 Figure 45.42 

 Magnetic time base 



The linearly rising current in L^ {Figure 45.41) suggests that a circuit along 

 the lines of the converter might be used as a time-base generator for a 

 magnetically deflected cathode ray tube. In fact this is quite possible; the 

 time-base circuit has the appearance of Figure 45.43, and has been used by 

 the author for an experimental transistorized oscilloscope. The energy in 

 the magnetic field following each growth has to be recovered from across 



Deflector coils 



t—nsM^ 



Sync ^ 

 current 



Sweep 

 amplitude 



Figure 45.43 



the winding Lj, by the crystal diode, capacitor and load as shown. A 

 moderately linear sweep is possible whose duration is adjusted by varying an 

 air gap in the iron core. The difficulty is to get the flyback time Tg i^i 

 Figure 45.44 short compared with T^. On a repetitive time base T, represents 

 'dead' time in which events will not be drawn on the cathode ray tube face 

 properly. It is not difficult to see that, ignoring for one moment the deflector 

 coils, the time ratio T-^jT.^ is equal to the ratio of voltages appearing across 

 L^„ F2/K1. For the current rise to be linear, the voltage dropped across the 



703 



